Multichip Modules (MCMs) are well known. A typical MCM includes a plurality of diverse elements disposed on one or more substrates enclosed within a molded housing. The diverse elements form an electronic circuit for, for example, driving a motor. Such circuits often include power semiconductor devices which may be connected to one another in a variety of ways.
A conventional circuit arrangement for driving a motor is known as a half-bridge. A half-bridge arrangement includes two power semiconductor devices connected in series. A typical power semiconductor device used in a half-bridge arrangement is a MOSFET, although other power semiconductor devices may also be used.
FIG. 1 shows a half-bridge arrangement using a pair of series-connected MOSFETs 10, 12. As shown in FIG. 1, the source electrode of MOSFET 10 is electrically connected to the drain electrode of MOSFET 12. In this configuration, input voltage Vin is connected to the drain electrode of MOSFET 10 while the source electrode of MOSFET 12 is grounded. The output voltage Vout is tapped at the connection node of MOSFET 10 and MOSFET 12. Typically, one or more schottky diodes 14 are connected in parallel with MOSFET 12 between the output node Vout and ground to minimize losses during dead time conduction period.
Half-bridge arrangements are vastly used in power supply devices. FIG. 2 schematically illustrates a conventional half-bridge arrangement in an MCM. Referring to these figures, according to a conventional arrangement, MOSFETs 10, 12 are disposed on a common circuit board 18. The circuit board 18 may be thermally conductive so that heat generated by the MOSFETs during operation may be transmitted to a heatsink (not shown) which may be placed in thermal contact with the circuit board 18. A suitable circuit board 18 may be an insulated metal substrate (IMS). As shown in FIG. 2, the drain electrode 10A, 12A, of each MOSFET 10, 12 is electrically connected to a respective conductive pad 22, 24 on substrate 18. To complete a half-bridge, source electrode 10B of MOSFET 10 is electrically connected to drain electrode 12A of MOSFET 12 through, for example a router, source electrode 12B of MOSFET 12 is connected to ground and drain electrode 10A of MOSFET 10 is connected to a voltage source as shown schematically in FIG. 2. Optionally, as shown in FIG. 2, a schottky diode 14 may be connected across drain electrode 12A and source electrode 12B of MOSFET 12 as is well known in the art.
Referring first to FIG. 3, another known MCM (disclosed in U.S. Pat. No. 6,946,740) includes a half-bridge circuit which is implemented by a pair of series connected power semiconductor devices one of which is a conventional device and the other one a flip-chip. The first one of the power semiconductor devices is a conventional vertical conduction power MOSFET 30 which has disposed on a first major surface thereof source contact 32 and gate contact 34, and on the opposing second major surface thereof drain contact 36. Drain contact 36 of power MOSFET 30 is electrically connected to conductive pad 38, by, for example, a layer of solder, or conductive epoxy. Conductive pad 38 is part of a printed circuit board 40. Printed circuit board 40 may be an insulated metal substrate (IMS), an organic laminate substrate, or direct-bonded copper (DBC) which includes a thermally conductive, but electrically insulative substrate 39 on which conductive pad 38 is disposed.
The other power semiconductor device is a flip-chip MOSFET 42. Flip-chip MOSFET 42 includes a drain electrode 44 on one major surface, and source electrode 46 and gate electrode 48 on an opposing major surface thereof. Source electrode 46 is electrically connected to conductive pad 50, while gate electrode 48 is electrically connected to conductive pad 52. Conductive pad 50 and conductive pad 52 are disposed on substrate 39 and form part of circuit board 40. Optionally, a schottky diode (not shown) is connected in parallel with flip-chip 42 between the output node and the ground in order to minimize losses during dead time conduction.
As schematically shown in FIG. 3, the half-bridge circuit is implemented by directly connecting source contact 32 of MOSFET 30 to drain contact 44 of flip-chip MOSFET 42 to obtain the series connection shown by FIG. 1. In the preferred configuration shown by FIG. 3, conductive pad 38 serves as the input connection Vin, while conductive pad 50 serves as the ground connection. The output connection Vout in the preferred embodiment is a point between source contact 32 of MOSFET 30 and drain contact 44 of flip-chip MOSFET 42.
FIG. 4 shows the top plan view of an MCM 54. MCM 54 includes a printed circuit board 40 on which a plurality of components C1, C2, C3, C4 are disposed. MCM 54 also includes conductive element 56. Conductive element 56 serves to connect a power semiconductor device, such as a conventional MOSFET 30 (FIG. 3), to a flip-chip semiconductor device such as flip-chip MOSFET 42 (FIG. 3), and also serves as the output connection according to the arrangement shown in FIG. 3. As is conventionally known, a molded housing 58 encapsulates all of the components disposed on circuit board 40. The circuit formed on circuit board 40 may be connected to external components via external leads (not shown) which may be disposed anywhere outside of the molded housing 58. For example, external leads may be disposed on the edges of MCM 54 or on the bottom surface of circuit board 40 in a ball grid array (BGA) or land array format.
FIG. 5 shows a cross-sectional view of MCM 54 along line 5-5 looking in the direction of the arrows. As seen in FIG. 5, MCM 54 includes conductive element 56. Conductive element 56 includes web portion 60 which connects drain contact 44 of flip-chip MOSFET 42 to source contact 32 of conventional MOSFET 30. As described before with reference to FIG. 3, source contact 46 of flip-chip MOSFET 42 is electrically connected to conductive pad 50 by a conductive layer 62 such as solder or conductive epoxy. Similarly, gate contact 48 of flip-chip MOSFET 42 is electrically connected to conductive pad 52 by a conductive layer 62. Drain contact 36 of conventional MOSFET 30 is also electrically connected to conductive pad 38 by a conductive layer 62.
Conductive element 56 also includes connector 64 which extends from an end thereof, and is electrically connected to conductive pad 66 by conductive layer 62. Web portion 60 and connector 64 are integral with one another.
In an MCM, conductive pad 66 serves as the output Vout (FIG. 3) of the half-bridge circuit, while conductive pad 50 and conductive pad 38 are connected to the ground and input Vin (FIG. 3) respectively.
In an MCM as described above, conductive element 56 is a relatively large metal body, which may be susceptible to solder joint fatigue and connector surface delamination.